February 2015

Animation 7: Jakobshavn Isbræ

I was planning on having a look at Jakobshavn Glacier some time later this season, but some recent developments made me decide to make an animation now. First off, some basic information from Wikipedia on one of the most important Greenland glaciers:

Jakobshavn Isbræ drains 6.5% of the Greenland ice sheet and produces around 10% of all Greenland icebergs. Some 35 billion tonnes of icebergs calve off and pass out of the fjord every
year. Icebergs breaking from the glacier are often so large (up to a kilometer in height) that they are too tall
to float down the fjord and lie stuck on the bottom of its shallower
areas, sometimes for years, until they are broken up by the force of the
glacier and icebergs further up the fjord.

Pictures say more than words. The MODIS image of Greenland on the right has a red circle in it showing where the glacier is located. The pictures on the left are aerial photos from glaciologist David Holland's webpage showing the icebergs calving from the ice front of the glacier, entering the waters of the Disko Bugt, and further up the glacier a picture of the terminus, located about 40 km up-fjord of the mouth.

Some more details from the Recession of Jakobshavn Isbræarticle on Mauri Pelto's Glacier Change blog, which I recommend reading in its entirety:

The Jakobshavn Isbrae (glacier) has captured our attention over the last
30 years because it has the highest long term average velocity of any
glacier in the world. At the ice front the velocity has remained above
16 meters per day for all measurements completed over the last 50 years.
The ability of this glacier which is 10 km wide at its front and 800 m
thick at the calving front to drain 6.5 % of the Greenland Ice Sheet is
its importance.

(...)

From 1964 to 2001 the glacier terminus did not recede significantly and
observations of terminus velocity remained relatively constant at 16 to
20 m year at the glacier front. Then in 1997 an acceleration began.
The velocity reached 34 m per day by 2003, twice its normal speed, the
glacier thinned by up to 15 m year and retreated 10 km, from 2001 to
2003. From 2004-2007 an additional retreat of 5 km occurred.

This picture is showing the retreat of the glacier terminus very nicely (click for a larger version):

NASA-funded researchers monitoring Greenland's Jakobshavn Isbrae glacier
report that a 7 square kilometer (2.7 square mile) section of the
glacier broke up on July 6 and 7, as shown in the image above [below, red.]. The
calving front – where the ice sheet meets the ocean – retreated nearly
1.5 kilometers (a mile) in one day and is now further inland than at any
time previously observed. The chunk of lost ice is roughly one-eighth
the size of Manhattan Island, New York.

(...)

As the glacier has retreated, it has broken into a northern and southern
branch. The breakup this week occurred in the north branch.

Scientists estimate that as much as 10 percent of all ice lost from
Greenland is coming through Jakobshavn, which is also believed to be the
single largest contributor to sea level rise in the northern
hemisphere. Scientists are more concerned about losses from the south
branch of the Jakobshavn, as the topography is flatter and lower than in
the northern branch.

Here's a close-up of the break-off (images courtesy of DigitalGlobe):

This image is an update from the previous one and has been annotated by Mauri Pelto (the A and the C). As Mauri comments below:

What is
fascinating is the speed at which the glacier surface below A at C was
transformed from an ordinary set of transverse crevasses to the chaotic
scene typically indicative of an area of rapid acceleration and failure
of seracs, those walls betweens crevasses. The glacier has had a
profound response to the rift. The area of crevasse transformation is
an indication of the connection of this area of the glacier to action at
the terminus. The area around C is a zone of weakness to watch for
further appearance of rifting. The area in front of the bedrock high is
clearly not a place for the terminus to stabilize. The bedrock high
itself could well be.

And now finally, the moment everyone has been waiting for, the purpose of this whole article: my animation of the last 7 days. I let them precede by day 172 and 178 to show what the glacier looked like a few weeks ago.

The part in the middle of the fjord with some water showing, looks
interesting. I was wondering if the fjord could clear entirely of ice if
conditions were right, and even asked Mauri Pelto's opinion on that in a comment on
his latest article, but to repeat part of the Wikipedia quote at the
start of the article:

Icebergs breaking from the glacier are often so large (up to a
kilometer in height) that they are too tall
to float down the fjord and lie stuck on the bottom of its shallower
areas, sometimes for years, until they are broken up by the force of the
glacier and icebergs further up the fjord.

So I don't think we'll be seeing that happening some time soon
(unfortunately, as it would look really cool).

I have also added two red circles on day 187 (July 6th) because unfortunately this is the best resolution we citizen 'scientists' can get from MODIS, and I had to look really hard to see where the change had taken place. The lower red circle is the area of the northern branch of the terminus where the rift and subsequent retreat takes place. The other red circle provides a orientation point that shows how the whole thing comes sliding down.

Okay, have a good look:

Just before publishing I decided to have a look at the latest MODIS image of this area (day 192) and was surprised to see some sort of local cloud hanging over the glacier and blocking the view. It looks a bit weird, perhaps caused by all the energy that is released when huge chunks of ice break off. So I've decided to add it to the animation. I'd love to hear how you folks interpret this weird cloud and what might be happening under it.

Update July 19th: the cloud was a trompe-l'œil, I've removed it along with some of the other cloudy images, and added the first cloudless day since over a week (day 199).

Here's a Youtube movie showing how such a sliding event or retreat looks like from up close (0.35 onwards):

Great stuff appears almost everyday in your examination. Having observed calving events on this glacier before, this is still astounding the size of it. Just inland of the rifting and current terminus is a bedrock high. As the glacier thins this will produce a greater weakening of the ice as it flow over. The rift formed directly downstream of this. I have annotated the NASA image and posted for your use . I note this location as point A. What is fascinating is the speed at which the glacier surface below A at C was transformed from an ordinary set of transverse crevasses to the chaotic scene typically indicative of an area of rapid acceleration and failure of seracs, those walls betweens crevasses. The glacier has had a profound response to the rift. The area of crevasse transformation is an indication of the connection of this area of the glacier to action at the terminus. The area around C is a zone of weakness to watch for further appearance of rifting. The area in front of the bedrock high is clearly not a place for the terminus to stabilize. The bedrock high itself could well be.

Neven: this is an excellent article which I shall soon be linking in my blog. Your animation captures the shift of melange nicely.

Ice breaks when the built up mechanical forces exceed its strength. At that time, the energy which caused the breaking is converted instantly into heat energy. This heat causes the formation of ice smoke, or where there is a lot of activity: a fog bank.

This glacier has now retreated past the union of two streams. That should cause further acceleration.

Thanks, logicman. I first learned of those ice smoke fog banks on your blog. :-)

Call me crazy but doesn't this mean there was another (large) retreat yesterday? Why would the ice smoke appear 5 days after the retreat between the 6th and 7th? I've been looking at the animation for the past 5 minutes and it certainly looks to me as if the dark patch on the right side, just above the bigger, lower red circle has shifted very far to the right implying a huge calving off.

But maybe I'm just seeing things here, it could just be the shadow of the fog cloud. Let's see if the Aqua satellite has made a new picture of the area yet.

I might have found something else to wet my alarmist appetite though: a second rift in the Petermann Glacier, halfway between the big rift and the terminus. If I have time I will look at it tonight. If true, the glacier will calve off spectacularly as soon as that sea ice in front of it gets washed away.

The fog is intriguing, but I would hesitate to jump to conclusions about why it formed. This area does have frequent fog forming by the usual means. We cannot even see the height of the cloud bank well. Down glacier winds are higher down the Jakobshavn too.

The loose ice near the pole in the MODIS imagery appears to be expanding and has mainitain itself for for about five days now. Enviornment Canada shows the sea ice temperture in that area as plus 2 as of yesterday. We now have a serious possibility of a polynya developing near or at the pole.

I would really like to see a PIOMAS update, as sea ice extent is really failing us as a tool in determining the actual ice loss. Even NSIDC which does a five day averaging, has done a hockey stick on us; indicating that sea ice extent is several deviations away from reality.

I was checking the grid size for NSIDC, and they count any cell with at least 15% coverage as sea ice for there calculations. Their grid size is 25km. Thats 625 sq km of ice per cell that can be misclassified per cell, and is obvious is, from the graph shown.

They give a paper with details:http://sharaku.eorc.jaxa.jp/AMSR/products/pdf/alg_des.pdf
Table 2 implies that they grid the data for sea ice concentration into 25 km, and also 12.5 km, data products. This grid size is a finer resolution than the measurements at 6.9 and 10.7 GHz (which actually give data at 58 and 37 km resolution). But the 89 GHz channel, for example, samples at 5km x 5km.

Another problem for Jakobshavn this year is the high snowline from the comparatively warm temperatures as evident in the June 17th snowline from Landsat compared to other years. The image is at the end of the post.

Excerpt : "In the winter of 2010, Jakobshavn’s ice front did not re-advance as it usually does, so it began the 2010 melt season in the same location as the 2009 summer melt season. As a result, the glacier had the potential to experience significant retreat during the summer of 2010. The breakup in early July 2010 occurred on the northern tributary to Jakobshavn Glacier. The southern tributary actually drains a larger portion of Greenland’s central ice sheet, so a retreat there could lead to a more substantial ice discharge."

Hi Neven,
Since I noticed your blogsite I check each day... This time I may have crossed something interesting while checking on todays Modis. Look at Kangerlussuaq glacier, King Christian IX land (straigt to the other side refering to J.Isbrae). You see the large swath of melting water ( 20x8 km)? Where did that come from... nothing there a day ago. Any opinions?

Hi Neven, Is this article still open for comments? Have you considered the link between NAO and retreating of the Jacobshavn glacier? Even intuitively, when the NAO is strongly negative, warm air and low pressures will come from the south accelerating the retreat of the glacier (together with general retreat of Arctic sea ice), while the positive phase of NAO should act to conserve sea ice and Greenland glaciers. The last two winters we have experienced extremely strong negative phases of NAO, which ties well with the lack of gain of the glacier, but here's the test; since we have seen a consistent positive NAO since Nov 2011, has the glacier been able to grow since then?

Should point out that so far as I'm aware, we can't know anything until the melt season. The glacier doesn't calve at all during the winter, so the floating tongue spends several months growing outwards undisturbed. Once the melt starts, it's a question of whether (and how fast) the calving front retreats back to the previous summer's line, or whether it'll stop short of that.